This invention relates to a water heater, and is more particularly directed to a water heater of the type having a main burner for heating a heat exchanger and a standing burner. This water heater also has an electromagnetic safety valve, which is opened by a manual operating member and which is kept in its valve open condition by an electric current from a thermocouple element which is exposed to the standing burner and a water pressure sensitive member such that it opens in response to a supply of water in the heat exchanger (that is, the water flow is turned on). Both the electromagnetic safety valve and the water pressure sensative valve are interposed in a fuel passage connected to the main burner. A standing burner fuel passage has one end connected to the standing burner and is connected at its other end to a point in between the two valves.
It has been usual with this type of water heater that, if the manual operation member is depressed, the electromagnetic safety valve is opened and at the same time an operation switch for an ignition device is closed, thereby igniting the standing burner. If, after the completion of this ignition operation, the heat exchanger is supplied with water, the water pressure sensitive valve is then opened by a water pressure responsive member, thereby the main burner is fired.
It is also known that this type of water heater may be provided with a control circuit which comprises a capacitor, a discharging circuit for the capacitor with a solenoid operating the safety valve, and a changeover switch adapted to be switched by the manual operation member between a charging condition where the capacitor is being charged by an electric power source and a discharging condition where the capacitor is connected to the discharging circuit.
The known water heater having this control circuit, however, is undesirable, because unburned fuel may be discharged from the main burner. When the electromagnetic safety valve is kept in its valve open condition by the action of the discharging circuit immediately after the manual operation member is operated, and if the heat exchanger is supplied with water under the condition that the standing burner is not yet iginited substantially simultaneously with the depression of the manual operation member or if the manual operation member is depressed under the condition that the heat exchanger is supplied with water, then both the electromagnetic safety valve and the water pressure sensitive valve are brought into their valve open condition. Consequently, despite the fact that the standing burner is not yet ignited, a large amount of gas is supplied to the main burner, resulting in a discharge of unburned gas.